基于磁导率法的零部件硬度电磁无损检测技术研究

Research on Nondestructive Testing Technique for Part Hardness Based on Magnetic Permeability Measurement

传统的机械压痕法虽能测量火炮零部件的硬度，但对其表面有损害，且某些零部件工作面并不允许使用打点测量方式．为解决这一问题，基于硬度与材料磁导率之间的对应关系，设计了一种硬度电磁无损检测系统，采用DDS技术实现参数可控的正弦信号源，以满足磁导率测试所需的激励条件．为了提高检测灵敏度，利用交流电桥拾取由硬度变化引起的检测线圈和参考线圈电压差分信号，并进一步在调理电路中采用正交锁相放大技术对这一微弱信号进行放大和噪声抑制．硬度试验结果表明，该系统能以无损的检测方式有效地区分零部件的硬度值，为火炮定型试验中的硬度测量提供了新途径．

Hardness of artillery parts can be tested using mechanical indentation method,but part surface is destructed. Besides, working face of certain parts can not be inspected with indentation. In order to solve this problem,electromagnetic nondestructive testing apparatus for hardness has been devised based on the relationship between part hardness and magnetic permeability. Direct Digital Synthesizer （DDS）technique is applied for realizing sinusoidal signal generator with parameter-adjusting,which meets the demand of magnetic permeability measurement. To increase the sensitivity, alternating-current Bridge is applied to output difference voltage of pickup coil and reference coil,which is caused by hardness change. Furthermore, the orthogonal lock-in amplifier （LIA）technique is used to amplify weak signal and suppress noise in the signal detection circuit. The experimental results show that this apparatus can be applied to test hardness of artillery parts nonde- structively. It is a new approach for hardness testing in the artillery design experimentation.